Method for geophysical prospecting



Feb. 1, 1949. K]TTQ 2,460,297

METHOD FOR GEOPHYSICAL PROSFECTING Filed Jan. 51, 1945v 5 Sheets- Sheet 1 FIJEIZ:

IN VEN TOR.

Feb. 1, 1949. I KlTTo 2,460,297

METHOD FOR GEOPHYSICAL PROSFECTING 5 Sheets-Sheet 2 Filed Jan. 31, 1945 Feb. 1, 1949. -ro 2,460,297

I METHOD FOR GEOPHYSICAL 'PROSPECTING Filed Jan. 31, 1945 5 Sheets-Sheet s Gal-M z m INVENTOR.

BY @MW Feb. 1, I F, -ov 2,460,297

METHOD FOR GEOPHYSICAL PROSPEGTING Filed Jan. 31, 1945 5 Sheets-Sheet 4 DKZMJM I N VEN TOR.

Feb. 1, 1949. F. KITTO 2,460,297v

METHOD FOR -GEOPHYSICAL PROSPECTING Filed Jan. 31 1945 5 Sheets-Sheet -5 FIE-.2 E.

Fizz-E111,

INVENTOR.

BY W

HTTOKM Patented Feb. 1, 1949 METHOD FQR GEOPHYSICAL PBOSPECTING Leicester F. Kitto, Glendale, Califi, assignor of one-half to Roderic Crandall, Roswell, N. Mex.

Application danuary 31, 1945, Serial No. 575,472

6 Claims.

This invention is a new and useful method for geophysical prospecting and is a continuation in part of my prior application, Serial No. 455,414 filed August 20, 1942, which, in turn, was a continuation in part of my application, Serial No. 368,554 filed December 4, 1940.

More specifically, the invention is a method for determining the existence and location of and for delimiting the extent of petroleum accumulations or reserves in the earth.

One object of the invention is a more direct and positive establishment of the existence and extent of a petroleum accumulation than is possible by prior methods. Another object of the invention is the establishment of the existence and extent of a, petroleum accumulation more speedily and more economically than is possible by prior methods.

I have discovered that when a detonation occurs in or immediately adjacent to the surface of the earth, there is a resulting change of an electrical character in the immediate vicinity of the detonation and this change is of a different order of magnitude and/or duration above an earth accumulation of petroleum than in other areas which are not above such anaccuinulation. I am unable to define or to indicate the nature of the electrical change. I have, however, been able to establish the existence of the same, and by extensive experimentation have been able to establish other facts which are essential to the interpretation and application of the same.

The application of my invention will be evident from the following description read in conjunction with the drawings, in which:

Fig. 1 is a longitudinal vertical section through an apparatus by which the detonation referred to may be produced and directed;

Fig. 2 is a diagrammatic plan of electrical apparatus by means of which the duration of the electrical change may be measured;

Fig. 3 is an enlarged side view of one element of the construction shown in Fig. 2;

Fig. 4 is an exploded section through a part of the construction shown in Fig. 3;

Fig. 5 is a side view with parts in section of a recording apparatus usuable in the place indicated for that purpose in Fig. 2;

Fig. 6 shows diagrammatically an alternative form of recording apparatus;

Fig. '7 shows diagrammatically another alternative form of recording apparatus;

Fig. 8 is a top 'view of a recording;

Fig. 9 is a top view of'another recording;

Fig. 10 is a chart showing a form of profile of readings extending from a generally non-producing area across a centrally located producing area;

Fig. 11 is a similar chart showing a slightly different form of profile which is at times encountered in practice, and

Fig. 12 is a chart showing an actual profile of readings obtained in passing from a non-producing area into a producing area.

Referring to Fig. 1, the apparatus 5 by which the detonation is controlled and directed, includes a steel cylinder 2 provided with breech block 3, shell chamber 4 and firing pin 5. Cylinder 2 is about 40" in length and 4 inside diameter. The side wall of cylinder 2 defines a number of holes -6 about 1" in diameter, the purpose of which is to vent the gases resulting from the explosion. Shell chamber it is for ordinary 12 gauge shot gun shells. In practice, a hole is drilled in the earth to a depth of about 18" and the cylinder is inserted therein as indicated in Fig. 1. It has not been found essential to carry the lower end of the cylinder below the over-burdened or weathered layer, but the test hole should be drilledin firm ground. Whenever it is desired to operate the detonation apparatus, shell '1 is inserted in chamber 4 and fired by firing pin 5 with hammer 8.

The specific size and proportions of the steel cylinders do not appear to be critical. I have obtained equally good results using a cylinder of the same length, but of three inches inside diameter and provided with a plug for the upper end in which there is axially fixed a 44/40 re volver, the muzzle of which discharges longitudinally into the cylinder. Since the revolver is automatic in operation, this particular form of detonating device enables me to carry out tests in more rapid succession than is possible with the apparatus shown in Fig. 1.

As hereinbefore stated, such a detonation produces a change of an electrical character in the vicinity of the detonation. The magnitude and/or duration of the change appear to be independent of the volume of sound produced. In ordinary work, the detonation should be projected directly downward. The change to be detected and recorded appears to be initiated by a violent chemical reaction of brief duration, such as takes place during an explosion of this character, or bythe effect of the actual mechanical concussion waves suddenly produced by the explosion on the earths electrical field at the point of detonation.

I am aware of the fact that explosive charges which may be of an amount of several kilograms, are used in seismographic prospecting to produce a seismic shock or concussion wave extending to and returning from a formation, the depth and dip of which is to be determined. While I am not precluded from the use of charges of this order, I do not require the same and obtain reproducible results by the use of charges of only several grams which are too small to produce substantial seismic shock which would penetrat to any substantial depth.

The effect obtained in seismographic prospecting is a refraction or reflection of the seismic wave by a geologic formation. This is picked up as a mechanical vibration after a finite interval following the shot" or concussion which vibration is caused by special instruments to vary the current in a closed circuit for the purpose of measuring the interval. The exact time of the intervening interval is in such cases a function of the velocity of travel and distance of the particular formation from the shot and from the instrument. In the application of my invention, however, not only is the "shot preferably so small that it cannot initiate a substantial concussion wave, but the change that I measured follows immediately the detonation, lasting only a fraction of a second, and where taken over an accumulation of petroleum, appears to be independent of the absolute depth of the accumulationand to be characteristic of the area immediately overlaying the accumulation. There does not appear to be any measurable interval between the shot and the change referred to and What I measure is the magnitude and/or duration of the electrical change. More specifically, the change that I measure has a component of relatively low pitch in the audio-frequency range. In the practical application of my invention, I measure the duration of the electrical change, and the maximummeasurable duration of the same is of the order of one-half a second. a e

Referring to Fig. 2, II designates an electrical pick-up and amplification circuit. Insofar as the amplification section of this circuit is involved, it is of the usual audio-frequency amplifying type employing in series two or more radiotrons such as 201As. Where a straight line record of the duration is essential, the last radiotron should be a detector so thatthe output will have a unidirectional component. The details of this section will be hereinafter described. Attention is directed to the pick-up section I2 of this circuit comprising battery I3 connected through lead I4 in series with element I5 into lead I6 and thence through milliamperes meter l1 andthence through primary I8 of transformer I9. Element I5 consists of solid non-metallic conductors in loose contact with one another through which a small current is caused to flow continuously by means of battery I3. The particular form of element I5 that I have found best suited is a device that has been heretoforelused as. a microphone and is shown in detail in Fig. 4.

Referring now to Fig. 4, 2| and 22 designate the parts of the external casin or shellwithin which the loosely contacting non-metallic conductors are housed, 23 designates a disc of carbon defining a number, about 6 in all, of hemispherical cavities 24, symmetrically disposed with respect to the center of the disc. Disc 23 is held in position by machine screw 25 which extends through shell portion 2I and is in turn secured by nut 26. Disc 24 restson metal disc 21 which in turn rests on paper disc 28. Electrical contact with metal disc 21 and carbon disc 23 is made by means of the screw 29 and nut 30, threaded thereto, which is in turn connected to lead I4 (Fig. 2). The cups, i. e., the hemispherical cavities 24, are filled with small carbon balls having a diameter of .8 to 1.0 mm. These are loosely charged and therefore gravitate to a position such that some are always in loose electrical contact with disc 3! which is of carbon highly polished in the central section. The hemispherical cups are of slightly larger diameter than the carbon balls and there is moreover some clearance between the surface of the balls and the disc 3|, so that the balls are at all times free to move slightly and are not under mechanical pressure. Clearance between disc 23 and the facing side of carbon disc 3| is about .002". Disc 3I is in electrical contact by means of lead 32 with binder post 34 which is in turn connected to lead I6 (Fig. 2). Disc 3| is held between suitable washers such as 35 and 36. When the unit is assembled, shell portion 22 overlaps shell portion 2| and is secured in this position by means of set screws 31 and 38.

The loose contact should not be metallically shielded and for this reason the shell portions 2I and 22 should not be of metal, but may, for example, be composed of a plastic, such as Bakelite. If they are of metal they should be principally cut away to expose the loose contact and in this case the machine screws 25, 29 and 34 should be electrically insulated from shell portion 2| by means of bushings such as 25', 29' and 34'.

Although I do incidentally take advantage of the capacity of the microphone to operate as such, its primary function in the application of my invention is not that Of a microphone but, pro contra, to measure the duration of electrical change immediately following the detonation. Whatever the character of the electrical change, it does appear to effect an alteration in the internal resistance of the loose contact of the microphone and this diminution in internal resistance appears to be definitely of greater measurable duration following a detonation above a petroleum reserve than following a detonation above a nonpetroleum-bearing area. The sound waves resulting from the detonation do produce an initial variation in the internal resistance of the microphone Which will register on the recorder used and which constitutes a convenient pulse or zero mark from which to measure the overall duration of the electric change which follows thereafter. I have, however, conducted thousands of experiments in this way over areas which were known to be barren of petroleum and over other areas which had been independently established to contain petroleum, and in this way have demonstrated fully that whatever may be, the cause of the change, where the detonation occurs above a petroleum-bearing area, there is a definite and measurable alteration in the internal resistance of the loose contact which immediately follows the detonation, and which, as stated, has an audiofrequency component of low pitch and which persists for finite period up to 0.5 second. That this eifect is not due to the microphonic reaction to the sound waves produced by the detonation is shown by the fact that in exhaustive experiments which I have conducted using microphones which do not contain loosely contacting non-metallic conductors such as crystal pick-ups and dynamic pick-ups, this effect is completely absent.

The duration of the change appears to be independent of the absolute depth of the accumulation and to be characteristic of the area immediately overlaying the deposit. The intensity of the change and the differential between the effect obtained over a petroleum accumulation, and elsewhere, are subject to a diurnal variation. This variation is not great enough to impair the usefulness of the invention but in order-to obtain comparative readings where tests are made throughout the daylight hours, the diurnal variation should be first established under'known conditions anda suitable correction applied to all readings to compensate for this efiect. It .is preferable to carry out-the tests during the hours of darkness and the early morning and late afternoon, Where comparable results are desired over an area so great that several hourswould be required for the completion of the work. The differential between the duration of the change overa petroleum accumulation comparedto the duration of the change overlaying an area beneath which there is no petroleum accumulation varies during those periods when the earth is subject to intense electronic bombardment associated with periods of abnormally high sunspot activity and during such periods the'difierential becomes irregular. The existence of such periods is, of course, determinable by other methods and, if possible, tests should not be conducted during the same. Where, however, the testing is carried out during the night, early morning and late afternoon and during a period'when the earths electrical field is not subjected to violent disturbances such as interfere seriously with radio communication, concordant and reproducible results will be obtained in which the 5'- The internal resistance of the loosely contactin non-metallic conductors should run between and 50 ohms and is preferably about ohms.

The E. M. F. of the battery i3 should be suificient to normally-carry a current of about milliamperes between disc 23 and disc 3!. In practice, a battery generating an E. M. Ref 1.5 v. has been found satisfactory.

Referring to the amplifying section, this includes the audio-frequency transformer l9 including primary winding 98 and secondary winding 52 and having a step up ratio of 200:1. One leg 53 of secondary winding is connected to grid 54, of radiotron 55 while the other leg 55 is connected through the grid bias C battery 5,? (E. M. F. 4.5 volts) to negative lead. 58 of the filament energizing circuit. The filament B! of radiotron 55 is energized by means of A battery 62 (E. M. F. 6 v.) feedin through manually controllable rheostat 53 to the negative lead 64 which is connected to one side of the filament 5i. The other side of filament (ii is connected through lead 65 back to the positive pole of filament energizing A battery 82. The current from plate 53' of radiotron 55 flows through lead 64' to the primary winding 65' of transformer I 56 and thence through lead 65 to the positive side of B battery $1 which in this specific embodiment of the device generates an E. M. F. of about 145 Volts. Secondary 68 of transformer 66 is connected through lead I! to grid 12 of radiotron 73. The other leg it of secondary 68 is connected through lead l5 to negative side of grid bias "0 battery 5?. The fixed resistance 59 of a value of 150,000 ohms is connected in shunt with secondary winding 68. One side of the filament T6 of radiotron 1'3 is'carried back to the rheostat 53 while the other side of filament ii is carried back to lead 65 and thence to the positive side of the filament energizing A battery 62. The plate H of radiotron i3 is connected through lead '58 to binder post l8 of recorder 88, which is any suitable recording device adapted to respond to electrical variation within the audio-frequency range, and thereby to record the duration and/or magnitude of said electrical variation. Where a unidirectional component is required for recording purposes, the place-of this last radiotron is taken by a detector tube with suitable modifications in the associated circuit or an additional detector tube is added after radiotron F3.

The other post 8! of recorder 89 is connected through lead 82 and through lead 56 back to the positive side of B battery 5'1. Variations in the current output of the amplifier are indicated by milliampere meter 83 in series in this circuit. Lead 82 is also connected to one side of the capacitance 84, the other side of which is con nected through the lead 85 to the negative side of the filament energizing circuit. This is of the order of 0.25 mid.

I have indicated the recorder 89 generically since I may use at this point any suitable device for recording electrical variations within the audio-frequency range.

One such recorder may for example be a string galvanomet'er coupled with means for projecting a light track onto a movin film. More simply,

this may be accomplished by passing the current from plate l1 through lead 58 and through floating coil 9| (Fig. 5) within the uniformly maintained field of electro-magnet 82. Floating coil 9! is pivotally carried at 93 and actuates light mirror 9 3 which directs a beam from light source 95 onto a photographic film moved at the uniform rate by any suitable means, not shown. In this case when the apparatus is not energized the light track recorded on film 96 is a straight line. The pulse or shock of the detonation picked up by element IE will appear on the film as a sharp and marked departure from the straight line track and the succeeding electrical change will appear as an oscillatory deviation from the straight line track, the overall length of which is functionally dependent upon the duration of the change, and the height of which is a function of the magnitude of the change. The comparative measurement of the duration of the change is obtained by comparing total lengths of light track which show oscillatory deviations from the straight line track.

Another such recorder is indicated diagrammatically in Fig. 6 in which .iili indicates a record suited to photographic recording and reproduc-- tion mounted on. a turn table moving about axis Arm ill-3 is mounted on case Hit and is adapted to swing about point m5. Although diagrammatically indicated, arm N13 is of the type adapted to out, i. e., to make sound track recording within the audio-frequency range on record it! and for this purpose it is operated as a recording device While the apparatus is in use. Thereafter, arm 5% can be changed from cutting adjustment to playing back adjustment or alternatively the record I! can be transferred to a turn table provided with the usual tone arm; in this case the sound of the electrical change will be recorded and on playing back will be audibly appreciable as a low rumble or grumble. Comparative measurements of the duration of the electrical change are in this case obtained by comparison of the duration of the rumble or grumble sound, while the magnitude is indicated by the volume of the same. This method has the disadvantage that it is not easy to spot the exact zero point of a number of runs in the record and it is not easy to make a direct comparison of the results obtained. This may be accomplished somewhat more easily by playing back at a much slower rate.

Another such recorder is indicated diagrammatically in Fig. '7, in which Hl is a motor drive adapted to rotate the turn table 1 i2 at a constant speed which inthe apparatus actually employed in my tests was 50 R. P. M. The turn table H2 carries a disc of paper. The stylus H3 is provided on the end of the lever H4 pivotally carried by the post I I5 at the point I I6. Normally, the lever H4 is held in the position indicated by dotted outline H! in which the stylus H3 does not contact the rotating disc of paper. The lever H4 is provided with the armature H8 within the field of the electro-magnet indicated diagrammatically as H9 provided with the coil H0. The leads l3! and I32 are connected to the posts 19 and 8| of the recorder 80. The lever H4 is under a very light tension supplied by the spring I33 and the amplifying apparatus shown in Fig. 2 is adapted to deliver a unidirectional component through the coil L30 whenever a current having variations within the audio-frequency range flows through the microphone !5. Whenever this occurs, therefore, the lever H4 is depressed and the stylus I It generates an are on the paper disc lying on turn table H2, the length of which is proportional to the time which the lever H4 was in the depressed position indicated in solid outline in Fig. 7..

Fig. 8 is a reproduction of a paper disc which has been inscribed in this manner in apparatus which operated to generate an arc on the disc proportional to the duration of the variations within the audio-frequency range flowing through microphone i5, and which was made on March 26, 1941, at 1:30 p. m. in the Baldwin Hills Oil Field, Los Angeles County, California, alongside a pumping well located in a producing sand. As noted, several tests were made and the average length of the readings is 8.22 inches, which corresponds to .3044 second.

Fig. 9 shows another disc which was similarly prepared on the same date at 1:40 p. m. .about 1000 feet southwest of the test shown in Fig. 8 above an area barren of petroleum, as shown by the fact that several dry holes had been drilled in this immediate territory, as the average length of the lines on this disc is 4 inches, which corresponds to a time of .1481 second.

These recordings are indicative of those made respectively over petroleum-bearing areas and areas barren of petroleum and were selected because these two spots have been frequently used to test the condition of the equipment.

In Fig. 10, I have shown in Cartesian coordinates a form of curve to which the readings made in accordance with my method very roughly correspond when passing from barren area to productive area. In this case, the 10 divisions of ordinates correspond to a total time of 0.4 second whereas each division of abscissa corresponds roughly to a linear distance of /2 mile. The area of long readings shown by the hump in the center of the chart indicates generally the type of readings encountered when passing over an area containing petroleum.

Another'form of curve differing somewhat from 5 that shown in Fig. 10 appears in Fig. 11. The respective values of the ordinates and abscissa are the same as in Fig. 10. As indicated on this curve when approaching the vicinity of the petroleum-bearing area from either side there is a slight drop in the duration of the readings. The reason for this is not fully understood but in passing directly over the petroleum-bearing area, the characteristic increase in the duration of the readings is obtained.

In practice, there are deviations from this idealized form of curve and in Fig. 12 I have shown a curve which is the locus of all readings made in moving from a non-producing area onto an actual producing area more specifically identified as Coles Levee Oilfield in Kern County,

California. In this case, the ten divisions of ordinates correspond to a total time of 0.4 second, whereas each 1 along the axis of abscissa equals mile.

I claim:

1. Method of prospecting for subsurface accumulations of petroleum, the steps of detonating an explosive charge adjacent the surface of the earth, maintaining adjacent the point of detonation an electrical circuit in which current is flowing through non-metallic solid conductors lightly contacting one another and unshielded in relation to the earth, amplifying variations in flow of current through said circuit following immediately and within not exceeding 0.5 second.

2. Method according to claim 1 in which the non-metallic solid conductors include at least one carbon sphere and a holder of carbon lightly contacting the same.

3. Method according to claim 1 in which the duration of such variations is recorded.

7 4. Method of prospecting for subsurface accumulations of petroleum, the steps of detonating an explosive charge adjacent the surface of the earth at numerous points over the area to be prospected, maintaining adjacent each point of detonation an electrical circuit in which current is flowing through non-metallic solid conductors lightly contacting one another and unshielded in relation to the earth, amplifying variations in flow of current through said circuit following im mediately, and within not exceeding 0.5 second.

5. Method according to claim 4 in which the nonmetallic solid conductors include at least one carbon sphere and a holder of carbon lightly contacting the same.

6. Method according to claim 4 in which the duration of such variations is recorded and com pared.

LEICESTER F. KITTO.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,001,429 McCollum et a1 May 14, 1935 2,051,153 Rieber Aug. 18, 1936 2,054,067 Blau et al Sept. 15, 1936 2,118,441 McCollum Ma 24, 1938 

